This invention relates to an optical tracking system for establishing a line of sight in accordance with a position command signal and, more particularly, to such a system which is stabilized against environmental vibrations and perturbations.
U.S. Pat. No. 4,881,800, the contents of which are hereby incorporated by reference herein, discloses an optical tracking and stabilizing system for use in an aircraft vehicle which tracks the movement of the pilot's helmet by developing a position command signal which causes the line of sight of the optical system to follow the line of sight of the pilot. In the disclosed system, a mirror is flexibly mounted to a rigid block which in turn is fixedly mounted to the inner gimbal of a pair of gimbals. A gyroscope having a spin axis aligned with the line of sight of the optical system is mounted to the rigid block to develop signals which are utilized to control movement of the mirror relative to the rigid block so as to nullify vibrations which emanate both from the gimbal system during the positioning of the rigid block and from the vehicle.
In the referenced system, a first error signal is generated and applied to the gimbal system to control movement of the rigid block relative to the vehicle and a second error signal is generated and applied to the mirror subassembly to control movement of the mirror relative to the rigid block. It would be desirable to provide an arrangement which requires only a single error signal to control both the rigid block gimbal set and the limited motion mirror subassembly. Further, if the rigid block gimbal set has appropriate performance characteristics, the limited motion mirror subassembly is not needed.
As described in the referenced patent, in order to track the input position command and isolate the line of sight from angular vibration of the vehicle, the optical tracking and stabilizing system must behave like a position servomechanism in the low frequency domain and like an inertial stable platform in the high frequency domain. It is therefore an object of the present invention to provide an optical tracking and stabilizing system of the type described which permits independent control of the low frequency response to position command inputs, permits independent control of the high frequency isolation of the line of sight from the vehicle angular vibration, and does not compromise the ability of the system to reject the effects of disturbance torques over the full range of the system's frequency bandwidth.